tìm x : (x-7) ²+(x+1) ² - (2x+1) × (x+1)=- 4 help me

Đáp án:

`(x-7)^2+(x+1)^2-(2x+1)(x+1)=-4`

`=>(x^2-14x+49)+(x^2+2x+1)-(2x^2+2x+x+1)=-4`

`=>x^2-14x+49+x^2+2x+1-(2x^2+3x+1)=-4`

`=>x^2-14x+49+x^2+2x+1-2x^2-3x-1=-4`

`=>(x^2+x^2-2x^2)+(-14x+2x-3x)+(49+1-1)=-4`

`=>-15x+49=-4`

`=>-15x=-53`

`=>x=53/15`

Vậy `x=53/15`